1. Field
The presently disclosed embodiments relate generally to devices for deterring dangerous creatures, and more specifically to an electronic shark deterrent.
2. Background
Each year there are about fifty to seventy confirmed shark attacks and five to fifteen shark-attack fatalities around the world. The numbers have risen over the past several decades but not because sharks are more aggressive: Humans have simply taken to coastal waters in increasing numbers. While sharks kill fewer than twenty people a year, their own numbers suffer greatly at human hands. Between twenty and one hundred million sharks die each year due to fishing activity, according to data from the Florida Museum of Natural History's International Shark Attack File.
Most attacks occur in nearshore waters, typically inshore of a sandbar or between sandbars where sharks feed and can become trapped at low tide. Areas with steep drop offs are also likely attack sites. Sharks congregate in these areas because their natural food items also congregate in these areas.
There are three major kinds of unprovoked shark attacks. By far the most common are “hit and run” attacks. “Hit and run” attacks typically occur in the surf zone with swimmers and surfers being the normal targets. The victim seldom sees its attacker and the shark does not return after inflicting a single bite or slash wound. In most instances, these are probably cases of mistaken identity that occur under conditions of poor water visibility and a harsh physical environment (breaking surf and strong wash/current conditions). A feeding shark in this habitat must make quick decisions and rapid movements to capture its traditional food items. When these difficult physical conditions are considered in conjunction with provocative human appearance and activities associated with aquatic recreation (splashing, shiny jewelry, contrasting colored swimsuits, contrasting tanning, especially involving the soles of the feet), it is not surprising that sharks might occasionally misinterpret a human for its normal prey. Upon biting, the shark quickly realizes that the human is a foreign object, or that it is too large, and immediately releases the victim and does not return. Some of these attacks could also be related to social behaviors unrelated to feeding, such as dominance behaviors seen in many land animals. Injuries to “hit and run” victims are usually life-threatening.
“Bump and bite” attacks and “sneak” attacks, while less common, result in greater injuries and most fatalities. These types of attack usually involve divers or swimmers in somewhat deeper waters, but occur in nearshore shallows in some areas of the world. “Bump and bite” attacks are characterized by the shark initially circling and often bumping the victim prior to the actual attack. “Sneak” attacks differ in having the strike occur without warning. In both cases, unlike the pattern for “hit and run” attacks, repeat attacks are not uncommon and multiple or sustained bites are the norm. Injuries incurred during this type of attack are usually quite severe, frequently resulting in death. These types of attack are the probable result of feeding or antagonistic behaviors rather than cases of mistaken identity. Most shark attacks involving sea disasters, e.g. plane and ship accidents, probably involve “bump and bite” and “sneak” attacks. Almost any large shark, roughly two meters or longer in total length, is a potential threat to humans.
Likewise, sharks and other aquatic creatures are frequently injured and killed by human activities. When commercial fishermen catch animals that are not their desired catch, they call those animals “bycatch.” These unwanted animals are then thrown back overboard dead, dying, or injured. An estimated fifty million sharks are caught unintentionally as bycatch in commercial fisheries every year. Some of the most troublesome fishing gears for sharks are longlines, trawls, and gillnets.
As many as one hundred million sharks are caught unintentionally as bycatch in commercial fisheries every year. Longlines, trawls, and gillnets prove to be some of the most problematic fishing methods, producing large numbers of shark bycatch. Often, these unintentionally caught sharks will illegally have their fins removed as the fins are too valuable for many fishermen to resist. Sharks can represent an unusually high percentage of the bycatch compared to other species because they are often the same size as the target species or they are attracted to the easy prey that have already been caught.
Longlines can extend eighty miles and have several thousand baited hooks attached to the line. Because longlines are set in the water and often left for extended periods, by the time the lines are taken in, the sharks and other marine life are often already dead. In cases when the sharks are still alive, to avoid a potentially dangerous situation, fishermen simply cut the sharks loose with line and hook still attached. Dragging huge nets, weighted by anchors, through the ocean or along the ocean floor is a method of fishing called trawling. This technique results in significant bycatch and habitat destruction. Gillnets are like invisible barriers hung in the water to catch fish by trapping and holding them. The fish become ensnared in the nets and when they try to escape by backing out, their gills become caught in the net. Unfortunately sharks and other non-targeted species also become entangled and are left to die. The World Wildlife fund estimates that twenty percent of shark species are endangered.
In addition to preventing harm to people from sharks and unintentional devastation of aquatic life by human activities, other applications for deterring sharks have emerged in today's environment. For example, fish farms and other commercial operations suffer significant loss of revenue due to normal feeding activity of aquatic creatures, while vacation resorts are increasingly safety conscious.
Various methods of deterring sharks have been attempted. Buoy devices, extended tethers, and the like have proven to be too bulky, non-portable, power inefficient or ineffective. Traditionally, deterrent devices having electronic pulses in the most effective 30 microsecond (us) range have not been viable due to power, voltage, and size constraints.
Thus, there is a need in the art for a low cost, compact, portable, power efficient, multi-purpose, effective device for deterring sharks and other aquatic creatures from harming people and causing commercial losses as well as for reducing bycatch and conserving our environment.